Infusion pumps often do not have an end-of-infusion detection system. Instead, an air-in-line alarm is provided in the event that the medication container becomes prematurely empty and air is present in the infusion line. However, many customers utilize the air-in-line alarm as a mechanism to detect when the medication container is empty rather than titrate an unknown quantity of drug containing fluid after the set volume to be infused (VTBI) is complete. Caregivers often struggle with delivering 100% of the prescribed medication to a patient because the diluent typically varies in volume up to approximately 10%.
Existing strategies for detecting air often involve the use of ultrasonic sensors that are physically located on opposite sides of a tubing segment. When fluid is present in the tube, propagation of the acoustic signal is efficient and produces a large electrical signal via the receiver circuit. On the other hand, the presence of air in the tube causes an acoustical open circuit which substantially attenuates the detected signal. In current practice, detection of air in the tubing segment is often performed on the basis of a simple (static) air-fluid boundary or threshold that is applied to the air sensor voltage signal. When the air sensor signal moves beyond the pre-defined air/fluid threshold, an alarm condition occurs and the IV infusion is paused.
However, when the medication container is emptied (i.e., EOB reached) during an infusion program, a transition occurs from delivery of fluid to air. A film of liquid trails the liquid front as it moves in the tube. This film can break up leading to a stationary fluid droplet formation between the ultrasound transducers that is large enough to create an acoustic short circuit, yet small enough to allow air to pass. This acoustic short circuit can produce an absolute sensor signal similar to that of a fluid, which will cause false indication of fluid in the line and fail to detect the EOB and air in the line.
Currently, there exist methods/algorithms that utilize plunger force sensor readings to detect the presence of air in a plunger chamber. Several pumps made by Hospira, Inc. involve the use of a cassette with a chamber that is compressed by an actuated plunger to pump fluid at a controlled rate from the drug container to the patient. The measured force during a pumping cycle is directly related to the type of fluid in the chamber. For instance, fluids are relatively incompressible and generate a higher and different force profile than air.
However, using the existing force algorithms for detecting EOB often leads to a large number of false positives since the medication type (e.g., frothy fluids), proximal/distal pressure change and other factors can cause variability in force sensor observations.
A system and method is needed to overcome one or more issues of one or more of the current infusion systems and methods in order to detect an EOB event or to determine whether air is in the infusion system.